Automatic document feeder and registration system therefor

ABSTRACT

A sheet feeder transports sheets from a sheet supply, such as a document tray, to a distant location, such as a registration position on the platen of an electrophotographic copier. A sensing device monitors a time period which starts when a sheet advancing mechanism is actuated and ends when a sheet reaches the distant location. An indication of abnormal operation is provided if the sheet does not reach the distant location within a preset time period. The preset time period is initially set at one period of time and subsequently set at a shorter period of time. The initial time period is longer to allow the sheets to become fully engaged with the sheet feeder after initial loading, while the subsequent period is shorter to provide a quicker indication of abnormal operation.

This application is a divisional of application Ser. No. 449,132, filedDec. 13, 1982, now U.S. Pat. No. 4,621,799.

BACKGROUND OF THE INVENTION

Document feeders which use endless conveyor belts to advance originaldocuments across the exposure platen of an electrophotographic copierare well known in the art. In feeders of the type shown in U.S. Pat. No.4,023,791 to Hori et al and U.S. Pat. No. 3,844,552 to Bleau et al, aplurality of transversely spaced belts advance the document to aregistration edge of the platen where fingers of a controllableregistration gate interdigitate with the belts to arrest the document.While the use of spaced belts and an interdigitating registration gatein this manner ensures reliable document registration, the belts alsoappear along the margins of copies made from smaller-than-normaloriginals. Document feeders such as that shown in U.S. Pat. No.3,747,918 to Margulis et al which use a single wide belt provided withspaced longitudinal sheet-engaging ridges share this drawback, owing tothe clear line between the ridges and the flat part of the belt. Stillother feeders such as disclosed in U.S Pat. No. 4,093,372 to Guentherwhich use a single flat belt to obviate this problem do so only at thecost of reliable document registration. Since the registration gatecannot interdigitate with the belt, the leading sheet edge will tend towork its way between the feed belt and the registration gate and beyondthe registration edge of the platen.

Bleau U.S. Pat. No. 3,910,570 discloses a document feeder in which aplurality of axially spaced pressure rollers interdigitating with theupwardly extending fingers of a retractable exit gate are urgeddownwardly against the lower run of the feed belt to ensure that theleading edge of the document remains in contact with the exposureplaten. May U.S. Pat. No. 4,247,095 discloses a similar arrangement inwhich, rather than separate axially spaced pressure rollers, a singlepressure roller with reduced-diameter portions opposite correspondingraised portions of a registration edge is used to urge the leading edgeof the document against the exposure platen. While these arrangementsmay reduce or eliminate the problem of background clutter referred toabove, they also introduce an undesirable amount of complexity into theoverall system.

Other problems arise from the use of a registration gate to aligndocuments along the registration edge of a platen. Since the documentsare advanced across the exposure platen at fairly rapid speeds, 75inches per second not being an uncommon figure, their sudden stop at theregistration edge requires large decelerative forces that can damage theleading edge of the document being fed. In addition, owing to thehigh-speed impact of the document against the registration gate, thedocument tends to rebound from the edge, resulting in misregistration.While these undesirable effects can be reduced somewhat by reducing thedocument speed, such a reduction in speed also reduces the copy rateobtainable using the document feeder

Still other problems associated with automatic document feeders of theprior art relate to the separating of individual sheets from a stack andthe advancing of them to the exposure station. Automatic feeders must beable to advance documents through, or to a registered position within,the copier exposure station in an extremely short period of time tomaintain a high copy rate, especially if the document must remainstationary in the exposure station for an appreciable portion of thecopy cycle while being scanned by a moving-mirror copier optics. One wayto increase the effective copy rate, shown in Fackler U.S. Pat. No.3,556,512, is to move a second document to a ready position, separatedfrom the stack and adjacent the exposure station, while a first documentis being scanned. Not only does this reduce the distance that documentsto be copied must be transported during the scanning return stroke, butit reduces additional delays due to slippage, since the document to becopied is already in the nip formed by opposing pinch members ratherthan awaiting separation from a stack by opposing feed and retardmembers or the like.

Although this disclosed system of feeding a second sheet to a ready, orpreregistered, position while a first sheet is being copied permits ahigher copy rate, certain problems remain. Since Fackler requiresadditional feed elements to advance the preregistered document to theexposure station, he introduces a discontinuity of gripping surfacesbetween the stack and the station. Not only does this obviously increasethe complexity of the overall feeder, but it also increases the chancesfor skewing, slippage or the like.

Caldwell U.S. Pat. No. 4,043,665 discloses a semiautomatic documentfeeder in which documents inserted manually past a switch sensor areadvanced to a preregistration position defined by gates just downstreamof a set of registration rollers initially retracted from the platenbelt. When a preceding document on the platen has been copied, theregistration rollers are moved into engagement with the belt to grip thepreregistered sheet, and the registration gates are simultaneouslyretracted to permit the sheet to be moved onto the platen. While such anarrangement locates preregistered documents in a nip formed by theplaten belt itself, it is still a relatively complicated arrangement,owing to the various gates and retractable rollers that must be actuatedat the proper time.

Guenther U.S. Pat. No. 4,093,372 discloses a recirculating documentfeeder in which the bottom sheet of a stack of documents is pre-insertedinto the nip formed by a pair of opposing feed rollers which areactuated to advance the sheet to the exposure platen. However, Guentherdoes not support the stack of documents at a location spaced from thefeed rollers, but rather maintains the stack in a shingled (i.e.,partially separated, partially overlapping) configuration to avoid thenecessity of opposing sheet-feeding and sheet-separating members. Notonly is such a configuration easily disturbed, but it imposes anadditional limit on the maximum number of sheets that can be containedin the stack while maintaining reliable operation. In addition, sinceGuenther provides a second, independently driven pair of opposing feedmembers between the first pair and the exposure platen, he subjects thesheets to a discontinuity in drive force as the sheets enter the secondnip.

Suzuki et al U.S. Pat. No. 4,009,957 discloses an electrophotographiccopier in which copy sheets are advanced into a preregistration nipformed by stationary, contacting registration rollers so as to bucklethe sheet in the nip. The rollers are subsequently driven to feed thepreregistered sheets to the transfer station of the copier. Suzuki et aldo not disclose such a preregistration arrangement in the context of adocument feeder, however, nor do they disclose a system in which sheetsare advanced to a preregistration position defined by a roller and abelt.

Hori U.S. Pat. No. 4,231,562 discloses a feeder similar in some respectsto that of Caldwell in which sheets are automatically fed from a stackto a preregistration position defined by a gate. The gate is immediatelydownstream of an initially open nip formed by drive rollers, which arecoaxial with a pulley supporting the platen belt, and a set of pressurerollers which are subsequently moved into engagement with the driverollers to advance the preregistered sheet to the platen. Since,however, documents are not advanced to the drive and pressure rollerswhile these feed members are in a nip-forming configuration, a feeddiscontinuity, and thus occasion for sheet damage, is introduced whenthe nip-forming members are ultimately engaged with each other.

Still another problem associated with document feeders of the prior artinvolves the detection of the misfeeding of sheets from a stack ofdocuments. It is common in the art, as shown, for example, in Burlew etal U.S. Pat. No. 4,078,087, to test for misfeed by examining adownstream sheet sensor after a predetermined time period has elapsedfollowing the actuation of a sheet-feeding member to advance a sheetfrom the stack. If the sheet has not reached the sensor within thepredetermined time period, a jam is presumed, and a fault declaredHowever, when a stack of documents is first placed in the document trayof the feeder, a substantial period may elapse before the stack hassettled into a position assuring adequate contact between the drivenfeed members and the sheet to be fed. If a time period is selected whichis short enough to detect jams before significant damage to documentsoccurs, that same time period may result in a premature declaration of afault due to a jam when the document tray is initially loaded.

FIELD OF THE INVENTION

This invention relates to apparatus for feeding documents one by one toan exposure station and, more particularly, to apparatus for feedingdocuments to the exposure platen of an electrophotographic copier.

DESCRIPTION OF THE PRIOR ART

In addition to the patents described above, the following references arepertinent in varying degrees to the subject matter of this disclosure.

Gardner et al U.S. Pat. No. 3,473,035 discloses a document feeder inwhich a feed belt having a sheet document electrostatically adheredthereto is slowed a predetermined distance before the leading edge ofthe sheet reaches an exposure position at which the belt is stopped.However, Gardner et al do not use a gate to stop the sheet at aregistration position, and rely instead on the timing of the beltdeactuation to stop the sheet at the desired point.

Fackler U.S. Pat. No. 3,556,512 discloses, in addition to the featuresmentioned above, the use of an encoding wheel coupled to a movingelement of the document feeder for controlling the timing of the varioussteps in the feed cycle. No suggestion is provided, however, as tooperating the feed elements at different speeds at various stages of theoverall cycle.

SUMMARY OF THE INVENTION

In accordance with one aspect, or feature, of our invention, anapparatus for advancing a sheet to a predetermined registration locationon an exposure platen includes a rotary member which supports a flatbelt adjacent the registration location to position the belt with aportion thereof adjacent the exposure platen, the adjacent belt portionextending substantially across the width of the exposure platen andbeing adapted to move the sheet toward the registration location. Therotary member is formed with one or more reentrant portions in axiallyspaced portions thereof to form corresponding corrugations in the belt,while barrier means are adapted to extend into the belt corrugations tointercept the sheet at the registration location. The belt is driven insuch a direction as to move the sheet toward the registration location.

According to another feature of our invention, the sheet is initiallyfed along the exposure platen at a first speed toward the registrationlocation at which the leading sheet edge is intercepted to arrest thesheet. Prior to the arrival of the sheet at the registration location,and preferably upon the movement of the sheet to within a predetermineddistance of the registration location, the sheet feeding is discontinuedat the first speed, either by discontinuing the drive entirely orpreferably by continuing the drive at a lower speed, to cause theleading sheet edge to be intercepted at the registration point at aspeed lower than the first speed. Preferably, the advance of the sheetto within a predetermined distance of the registration location issensed by counting position pulses generated by an encoding wheelrotating synchronously with the movement of the sheet.

In yet another aspect, our invention contemplates apparatus for feedingdocuments to an exposure station from a stack in which a pair ofopposing feed members having a nip-forming configuration in which theyform a sheet-receiving nip are arranged on a path leading to the stationat a location spaced from the document stack. Preferably one of the feedmembers comprises a belt having a portion overlying the exposure platen.Documents are individually advanced from the stack to the opposing feedmembers while in their nip-forming configuration to inject the documentsinto the nip, and means are operable only subsequent to the injection ofa document into the nip for driving the feed members to advance thedocument to the exposure station.

In yet another aspect, our invention contemplates apparatus in whichmeans such as cooperating feed and retard members are adapted to beenergized to advance a sheet from a stack to a location spaced therefromand in which means are provided for gripping the sheet at that locationto continue to advance the sheet. The first advancing means isdeactuated following the arrival of the sheet at the location of thegripping means, but is momentarily reactuated prior to the emergence ofthe sheet from the first advancing means to ensure separation of thesheet from the remaining sheets in the stack.

According to yet another aspect of our invention, a first time period isinitially set within which a sheet fed from the document tray must reacha downstream jam sensor, after which a second time period shorter thanthe first period is set for the feeding of sheets between the samelocations. The first time period is selected to be long enough to allowa stack of originals to become fully engaged with the feed members afterinitial tray loading, while the second time period is sufficiently shortto detect jams in time to prevent appreciable damage after the originalshave become fully engaged. Preferably the changeover between the longerand shorter time periods occurs after the feeding of a first sheet froma newly loaded stack of documents, since it is at this point that therequirement of synchronizing with the copier timing imposes anadditional constraint on the amount of time allowable. By successivelyemploying two different time periods in this manner to determine thepresence of a jam, one is able to detect most jams rapidly enough toprevent damage to documents, while at the same time preventing prematurefault detection at the time that the stack is initially loaded.

OBJECTS OF THE INVENTION

One object of our invention is to provide a document feeder for anelectrophotographic copier which reliably registers documents at apredetermined position upon the copier exposure platen

Another object of our invention is to provide a document feeder for anelectrophotographic copier which produces copies with clear backgroundsfrom smaller-than-normal originals.

Still another object of our invention is to provide a document feederwhich does not damage the original documents being handled.

Another object of our invention is to provide a document feeder whichminimizes feed time, and thus maximizes the effective copy rate.

Still another object of our invention is to provide a document feederwhich ensures reliable feed and minimizes delay occasioned by slippage.

A further object of our invention is to provide a document feeder whichminimizes discontinuities occasioned by transitions between differentgripping surfaces.

A still further object of our invention is to provide a document feederwhich is especially adaptable for use with a copier in which originalsmust remain stationary during an appreciable portion of the exposurecycle.

Yet another object of our invention is to provide a document feederwhich is simple in construction.

Another object of our invention is to provide an original documentfeeder which detects jams rapidly enough to prevent damage to originalsbeing fed.

Still another object of our invention is to provide an original documentfeeder which does not declare a fault due to a sheet jam prematurelyupon initial loading or improper placement of sheets in the documenttray.

Other and further objects will be apparent from the followingdescription.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings to which reference is made in the instantspecification and in which like reference characters are used toindicate like parts in the various views:

FIG. 1 is a top plan of our automatic document feeder, with parts brokenaway.

FIG. 2 is a longitudinal section of the feeder shown in FIG. 1illustrating the placement of the feeder relative to the exposure platenof the copier with which it is used.

FIG. 3 is a rear elevation of the feeder shown in FIG. 1, with partsbroken away and with other parts shown in section.

FIG. 4 is a fragmentary top plan, rotated 90° clockwise from the view ofFIG. 1, of the registration gate assembly associated with the feedershown in FIG. 1.

FIG. 4A is a fragmentary top plan of an alternative form of registrationgate to the one shown in FIG. 4.

FIG. 5 is an enlarged section, taken along line 5--5 of FIG. 4,illustrating the positions of the registration gate fingers relative tothe exposure platen and copier exit guide in the raised and loweredpositions of the gate.

FIG. 6 is a fragmentary section, further enlarged from the view of FIG.5, showing the relation of the mating surfaces of the registration gateand exposure platen in the raised position of the gate.

FIG. 7 is a fragmentary section, taken along line 7--7 of FIG. 4,illustrating one of the retraction springs and the actuating rod of theregistration gate assembly of FIG. 4.

FIG. 8 is a fragmentary section, taken along line 8--8 of FIG. 1,illustrating the tray and entry sensors of the feeder shown in FIG. 1.

FIG. 9 is a fragmentary section illustrating the exit sensor of thefeeder shown in FIG. 1.

FIG. 10 is an enlarged fragmentary section, taken along line 10--10 ofFIG. 2, illustrating the extension of the gate fingers into thecorrugations formed in the platen belt in the raised position of theregistration gate.

FIG. 11 is a fragmentary left-side elevation of the feeder shown in FIG.1, with parts broken away and with other parts omitted.

FIG. 12 is a schematic block diagram of a control circuit for the feedershown in FIG. 1.

FIG. 13 is a flowchart illustrating the overall sequence of operation ofthe feeder shown in FIG. 1.

FIG. 14 is a flowchart illustrating the sequence of operation of theprefeed subroutine of the feeder shown in FIG. 1.

FIGS. 15a and 15b constitute a flowchart illustrating the sequence ofoperation of the feed subroutine of the feeder shown in FIG. 1.

FIG. 16 is a flowchart illustrating the sequence of operation of the jamroutine of the feeder shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, a document feeder incorporating thepresent invention, indicated generally by the reference numeral 20, hasan operative position shown in FIG. 2 in which it overlies the exposureplaten 24 of an electrophotographic copier, shown fragmentarily in FIG.4 and indicated generally by the reference numeral 22. The feeder 20includes a pair of transversely spaced rear and front sidewalls 26 and28. Respective support rods 30 and 32 support the feeder 20 for pivotalupward movement about an axis parallel to the lower edges of sidewall26, as shown in FIG. 11, to provide access to the platen 24 for copyingthick originals such as books.

The lower transport assembly of the feeder 20, indicated generally bythe reference numeral 34, includes a unitary conveyor belt 36,preferably formed of the cloth-based synthetic rubber sold by E. I.duPont de Nemours & Co. under the trademark Hypalon, having a highlyreflective white outer surface. An intake roller 38 disposed across theleft end of the exposure platen 24 as viewed in FIG. 2 and an exitroller 42 disposed across the right end of the exposure platen 24support the belt 36 in the operative position of the feeder 20 with thelower run of the belt in contact with the upper surface of the platen.Intake roller 38 is supported by a shaft 40 rotatably received byrespective sidewalls 26 and 28, while exit roller 42 is supported by ashaft 44 also rotatably received by respective sidewalls 26 and 28. Anidler roller 46 rotatably supported on a shaft 48 presses against theupper run of belt 36 between end rollers 38 and 42 to tension the belt.

Belt 36 receives originals to be fed to the exposure platen 24 from anupper transport assembly, indicated generally by the reference numeral50, in which a stack S1 is carried by a supply tray 52 mounted betweensidewalls 26 and 28 above the exposure platen. Tray 52 has an endadjacent the upper portion of roller 38, and is inclined upwardly awayfrom that end to bias documents in the stack S1 toward the upper portionof roller 38. A pair of axially spaced feed rollers 66, supported on ashaft 68 beneath the feed path from the stack S1 to the roller 38,cooperate with end retarding rollers 70 and a low-friction centerrestricting roller 74, supported by a shaft 72 on the upper side of thesame feed path, to ensure the feeding of only a single sheet at a timefrom the stack S1 to the roller 38. Feed rollers 66 have a relativelyhigh coefficient of friction, while retarding rollers 70 have acoefficient of friction that is lower than that of the feed rollers 66but higher than that between two contacting sheets of paper. As is morefully described in U.S. Pat. No. 4,231,562 to Hori, restricting roller74 extends radially into the gap separating the two feed rollers 66 tocorrugate the sheet of paper being fed to give it a degree oflongitudinal rigidity.

Feed rollers 66 are driven in a counterclockwise direction as viewed inFIG. 2 to advance the lowermost sheet of the stack S1 between rollers 66and rollers 70 and 74, while rollers 70 and 74 are also driven in acounterclockwise direction to urge any additional sheets that may havepassed between the rollers back in the direction of the stack S1.One-way couplings (not separately shown) between feed rollers 66 andtheir associated support shaft 68 permit freewheeling counterclockwiserotation of rollers 66 relative to shaft 68 to permit their overdrive bythe downstream sheet-feeding elements to be described, which are drivenat a slightly greater surface velocity. To ensure that sheets in thestack S1 are urged in the direction of rollers 66, 70 and 74, aplurality of conveyor belts 54 are provided at spaced locations acrosstray 52. Belts 54 are each supported by a first pulley 58 carried by ashaft 60 adjacent rollers 66, 70 and 74 and by a second pulley 62carried by a shaft 64 remote from rollers 66, 70 and 74. Belts 54 extendupwardly through respective slots 56 formed in tray 52 to contact thelowermost sheet in the stack S1. Pulleys 58 and 62 are drivencounterclockwise as viewed in FIG. 2 to urge the lower sheet in thedirection of rollers 66, 70 and 74. A guide 76 extending betweensidewalls 26 and 28 forms an acute angle with the stack S1 supported bytray 52 to define a throat into which the sheets in stack S1 are urged.Guide 76 is formed with fingers 78 that extend between roller shafts 68and 72 to define a clearance gap with feed rollers 66 of approximately 3millimeters.

After a sheet advanced from the bottom of the stack S1 passes betweenfeed rollers 66 and retard rollers 70, a semicircular guide 80 directsthe sheet around the periphery of roller 38 into a registration nipformed by belt 36 and resilient registration rollers 82 carried by ashaft 84. Registration roller shaft 84 is in turn received by a pair ofpivot arms 86 mounted on pivot screws 88 carried by sidewalls 26 and 28and biased in the direction of belt 36 by means of torsion springs 90associated with the respective arms 86. Belt 36 remains unactuated whilethe sheet approaches the registration nip to allow the leading sheetedge to fully enter the registration nip to ensure effectiveregistration. Feed belts 54 and feed rollers 66 remain actuated for asufficient time to allow the leading sheet portion to become buckledslightly in the region of the registration nip. After the originalemerges from the preregistration nip formed by rollers 82 and belt 36,it is directed further around the intake roller 38 to the imaging platen24.

As shown in FIG. 10, the roller 42 located at the exit end of theexposure platen 24 is formed with reduced-diameter or re-entrantportions 92 at spaced locations along its length to form correspondingindentations or corrugations in the outer surface of the adjacentportions of belt 36. The corrugations in belt 36 receive respectiveupwardly projecting integrally formed gate portions, or fingers, 94a to94e of a registration gate indicated generally by the reference numeral96, extending across the exit end of the exposure platen 24.

Referring now particularly to FIGS. 4 to 7, the exposure platen 24 isformed at its right end as viewed in FIGS. 2 and 5 with an oblique,upwardly facing registration edge 98 to ensure evenness of exposure ofthe adjacent portion of the document presented to the platen. Fingers94a to 94e, which are mounted for movement as a unit in a directionparallel to the surface of registration edge 98 (FIG. 5), extendupwardly out of slots 100 formed in a lower exit guide 102 carried bythe frame of the copier 22. Tension springs 104 extending between lugs108 carried by the exit guide 102 and lugs 106 carried at opposite endsof the registration gate 96 normally bias the fingers 94a to 94e to aretracted position shown in solid lines in FIGS. 4 and 5 with thefingers fully inside the slots 100. Actuation of a solenoid 110 carriedby the copier 22 in front of platen 24, as shown in FIG. 4, causes abell crank 112 to rotate clockwise about its pivot axis, drawing in turnan actuator rod 114 extending along registration edge 98 to the left asviewed in FIG. 4. This movement of actuator rod 114 in turn causesclockwise rotation of individual bell cranks 116 associated withrespective fingers 94a to 94e about their pivots 118. Upon this movementof bell cranks 116, cams 120 carried by bell cranks 116 bear againstcamming surfaces 122 of the fingers 94a to 94e to urge the fingersupwardly, in the direction shown in FIG. 5, to a blocking positionindicated by the dot-dash position 94b' of finger 94b shown in FIG. 5.

Camming surfaces 122 may extend either along a line parallel to theregistration edge 98, as shown in FIG. 4, or obliquely thereto as in thealternative construction shown in FIG. 4A.

As shown in FIG. 6, each of fingers 94a to 94b is formed with a verticalregistration surface 124, the lower edge of which is flush with theupper surface of exposure platen 24 in the blocking position of thefingers 94a to 94e. Each of fingers 94a to 94e is also formed with ahorizontal upper surface 126; the height of which above the uppersurface of exposure platen 24 in the upper position of the gate 96 issuch as to permit the fingers 94a to 94e to interdigitate with thecorrugated, or re-entrant, belt portions shown in FIG. 10. Preferably,surface 128 of fingers 94a to 94e adjacent to the oblique registrationedge 98 forms a slight angle with that registration edge, as shown inFIG. 6. Also, fingers 94a to 94e are preferably formed with a projectionor catch 130 below mating surface portion 128 to define the upper,blocking position of the gate fingers.

Referring now to FIG. 5, lower exit guide 102 is formed with a guidesurface 132 extending upwardly away from the oblique registration edge98 of the exposure platen 24 to guide sheets from the platen toward theexit rollers of the feeder 20, to be described. Preferably, the guidesurface 132 includes recessed portions 134 in the regions of the slots100, as shown in FIGS. 4 and 5, to prevent the leading edges of theguide surface 132 from interfering with the delivery of a sheet.

After exposure, solenoid 110 is deactuated to return the registrationgate 96 to a retracted position to allow belt 36 to deliver the sheet toan output tray 168 disposed above the upper run of belt 36 betweensidewalls 26 and 28. Respective inner and outer exit guides 140 and 142guide the sheet along a semicircular upward path between the exposureplaten 24 and the output tray 168. To ensure the complete emergence ofthe sheet at the upper end of the exit path, a first plurality ofopposing inner and outer exit rollers 144 and 148 are provided at onelocation along the exit path, and a second plurality of opposing innerand outer exit rollers 146 and 150 are provided at a second locationalong the exit path spaced downstream from the first location.Respective shafts 152 and 154 rotatably received by sidewalls 26 and 28support inner exit rollers 144 and 146, while shafts 156 and 158,rotatably received by respective pairs of pivot arms 160 and 162 carriedby spaced pivots 164 support rollers 48 and 150. Respective tensionsprings 166 coupling respective adjacent pairs of pivot arms 160 and 162bias outer exit rollers 148 and 150 against the corresponding inner exitrollers 144 and 146. Referring to FIG. 3, exit roller shafts 152 and 154extend past sidewall 26 to receive respective pulleys 246 and 248,coupled by means of an 0-ring belt 244 to a pulley 242 carried by exitroller shaft 44.

Tray 168 includes a top cover 170, preferably comprising a translucentplastic, supported by shaft 64 for upward swinging movement to retrieveoriginals stacked in the tray. Preferably tray cover 170 is formed withspaced longitudinal ribs 172 along its underside which guide theoriginals from exit rollers 146 and 150 onto the stack in the lower tray168 while minimizing electrostatic interaction between the sheets andthe tray cover. If desired, the upper tray 52 may have similar ribs 174along its underside, as shown in FIG. 2, to extend the effective guidesurface formed by ribs 172. Preferably tray cover 52 is formed with adownwardly extending edge portion 176 to prevent documents delivered tothe tray 168 from being re-fed to the platen by feed rollers 66.

To ensure the frictional engagement of a sheet of paper by the belt 36to move the sheet to the right across the exposure platen 24, as viewedin FIG. 2, we provide a pair of longitudinally spaced pressure rollers178 and 180 supported by respective shafts 182 and 184. A first pair oftransversely spaced pivot arms 186 carried by a shaft 190 extendingtransversely between feeder sidewalls 26 and 28 support roller shaft182, while a second pair of transversely spaced pivot arms 188 alsocarried by pivot shaft 190 support roller shaft 184. Pressure rollers178 and 180 are biased by their own weight and that of their associatedsupport assemblies to urge the adjacent portion of belt 36 against theplaten 24 and hence against any sheet that has been moved into exposureposition.

Sheets placed on the upper tray 52 are guided along one edge by sidewall28 of the feeder 20 and along the opposite edge by edge guides 192 and194 mounted on the upper tray 52 and lower tray cover 170, respectively.In the system contemplated, letter-size (81/2×11 inch) sheets are fedwidthwise, while legal-size (81/2×14 inch) sheets are fed lengthwiseboth in the feeder 20 and the copier 22. To accommodate the varioussheet orientations, as well as to allow for different sheet widths, edgeguides 192 and 194 are transversely adjustable with reference to thedirection of sheet feed along rods 196 and 198, which are carriedbeneath upper tray 52 and lower tray cover 170, respectively, and areprovided at several points along their lengths with detentscorresponding to various standard sheet sizes. It will be apparent fromthe foregoing description that lower tray cover 170 effectively servesas an extension of the upper sheet tray 52, owing to the flexibility ofthe sheets forming the stack. At the same time, however, tray cover 170does not increase the vertical profile of the feeder 20, since itextends purely horizontally in its lowered position.

Referring now particularly to FIGS. 1 and 3, feed rollers 66 and belts54 receive their drive power from a prefeed motor 200 mounted outboardof feeder sidewall 26. Motor 200 drives a gear box 202 having an outputshaft 204 carrying a pulley 206. A timing belt 208 couples motor pulley206 to a pulley 210 carried by retarding roller shaft 72 as well as to apulley 212 carried by feed roller shaft 68. Referring now particularlyto FIG. 1, retarding roller shaft 72 also carries a pulley 214 outboardof feeder sidewall 28. An O-ring belt 218 couples pulley 214 to a pulley216 carried by the shaft 60 supporting tray belt pulleys 58.

The lower belt 36 overlying the exposure platen 24 receives its drivingpower from a separate belt motor 220. Belt motor 220, which is disposedoutboard of feeder sidewall 26, carries a pulley 222 coupled by a timingbelt 224 to the input pulley 226 of an electrically controlled clutch230. A timing belt 232 couples the output pulley 228 of clutch 230 to apulley 234 carried by intake roller shaft 40. An encoder disk 236 alsocarried by intake roller shaft 40 contains a plurality of equally spacedapertures 238 about the peripheral portion thereof, which apertures areswept between the light source and photodetector portions of an opticalsensor 240. Optical sensor 240 is thus exposed to a beam of light eachtime the shaft 40 rotates through a predetermined angular displacement.Since the angular rotation of shaft 40 determines the lineardisplacement of the belt 36 and commonly driven feed elements, opticalsensor 240 produces pulses synchronous with the movement of each ofthese feed elements through a predetermined incremental distance. Byvirtue of this arrangement, the position of the leading edge of thesheet being fed may be determined regardless of fluctuations in theinstantaneous speed of the belt 36. In the description that follows, itis assumed that the normal belt velocity is 75 inches (1.90 meters) persecond and that the encoder pulse interval at this belt velocity is 2.5milliseconds An encoder pulse thus represents 4.76 millimeters of sheettravel.

Rather than employing separate motors 200 and 220 to drive feed rollers66 and platen belt 36, it is of course possible to use a single motor inconjunction with suitably actuated clutches to energize the various feedelements at the proper time. We have found, however, that if the feedrollers 66 are deactuated simply by disengaging a clutch coupling themto a motor, there is a tendency for additional sheets to be driven outfrom the stack following the emergence of the trailing edge of the firstsheet, owing to the rotational inertia of the feed elements. However, ifthe feed rollers 66 are directly driven from the prefeed motor 200, thedamping effect of the motor 200 when deactuated is sufficient tominimize or eliminate this tendency.

Referring now particularly to FIGS. 1 and 8, the sheets on the uppertray 52 are sensed by means of a pivoting bell crank 250 carried by apivot 256 mounted inboard of feeder sidewall 28. Whenever the tray 52 isempty, the bell crank 250 drops to the position shown in solid lines inFIG. 8, in which the lower arm 252 of the bell crank extends through aslot formed in the lower tray 168 and the upper arm 254 blocks the lightpath of an optical sensor 258 also mounted inboard of feeder sidewall28. When, however, the leading edge of a stack of sheets resting on theupper tray 52 protrudes into the nip formed by rollers 66 and 70, thesheets push the bell crank 250 upwardly to move the upper arm 254 to theposition 254' shown in dot-dash lines in FIG. 8 out of the light path ofoptical sensor 258.

An entry sensor 260 comprising a light source 262 and a photodetector264, preferably disposed adjacent the feeder sidewall 28, senses sheetsapproaching the preregistration nip formed by preregistration rollers 82and belt 36 to intercept the light path between the light source and thephotodetector. In a similar manner, referring now to FIG. 9, an exitsensor 266 comprising a light source 268 and a photodetector 270disposed on opposite sides of the exit path from platen 24 senses thepresence of documents in the exit path leading from the platen 24. Traysensor 258, entry sensor 260 and exit sensor 266 are used in a manner tobe described to control the timing of the feeder drive elements as wellas to sense the presence of a jam.

Referring now to FIG. 11, feeder 20 is mounted for pivotal movementrelative to the exposure platen 24, along a line of swinging movementindicated by the arrow 278, to permit the copying of thick originalsplaced manually on the platen 24, as well as to extricate any documentsthat may have become jammed as they are moved along the platen by thefeeder 20. More particularly, spaced pillars 276, one of which is shownin FIG. 11, receive respective brackets 272 for rotation about a pivot274. Brackets 272 in turn carry respective support rods 30 and 32 whichare received by the feeder sidewalls 26 and 28. Raising the feeder 20 apredetermined distance from the platen 24 closes a normally open switch290 having a fixed contact carried by one of the pillars 276 and amovable contact carried by a bracket 272. Switch 290 provides a signalto the control system to be described indicating the position of thefeeder 20 relative to the platen and, in particular, is used to generatea reset signal following the clearance of a jam.

Referring now to FIG. 12, the control circuit for the automatic documentfeeder 20, indicated generally by the reference numeral 280, includes aprogrammed digital computer 282 of any suitable type known to the art.Computer 282 may comprise either a microcomputer, such as an Intel 8048,having internal data and program memories (not separately shown) or amicroprocessor, together with separate program and data memoriesPreferably, if copier 22 is also to be computer-controlled, the samecomputer, whether a microcomputer or a microprocessor with externalmemories, is used to control both the feeder and the copier. It shouldbe emphasized, however, that the logic control units for the copier 22and feeder 20 may be entirely separate if desired and that the internalstructure of the copier logic as such forms no part of the presentinvention.

Computer 280 provides control signals to the electromechanical devicesof the feeder 20, including the prefeed motor 200, the belt motor 220,the belt motor clutch 230, the registration gate solenoid 110, and a"jam" display 288 of any suitable type known to the art. In the case ofbelt motor 220, computer 282 supplies suitable control signals toenergize the motor 220 at either a high speed or a low speed, or tode-energize the motor 220 entirely. Computer 282 also receives inputlines from the various sensors of the feeder 20, including the uppertray sensor 258, the entry path sensor 260, the exit sensor 266 and theoptical sensor 240 adjacent the feeder encoder disk 236 Preferably,sensor 240 is coupled to an internal counter (not separately shown) ofthe computer 282 through an interrupt input to allow the counter to beindexed by the encoder pulses in the course of the execution of the maincontrol routine.

In addition to these inputs from the various sensors of the feeder 20,computer 282 receives an input from a print switch 284 which is actuatedby the operator to initiate the automatic feeding operation Computer 282also responds to an end-of-scan signal provided by a suitable device 286of the copier 22 indicating the completion of exposure of a documentplaced on the platen 24. The end-of-scan signal may be derived in anymanner known to the art. Thus, if the apparatus shown in Suzuki et alU.S. Pat. No. 4,009,957 is used for the copier 22, the end-of-scansignal may be derived from the scan return switch Sw5 or Sw6, dependingon the length of the scanning stroke. Alternatively, if the copier 22itself is computer controlled, the end-of-scan signal may be derived byusing an encoder disk similar to disk 236 in the copier drive andcounting a fixed number of pulses following a predetermined cycle event,such as the return of the optical scanner to its home position.

Referring now to FIG. 13, the main routine followed by computer 282 forcontrolling the operation of the automatic document feeder 20 initiallywaits until the operator presses the feeder print switch 284. When thisoccurs, the routine calls the PREFEED subroutine shown in FIG. 14, whichadvances a sheet from the bottom of the stack on tray 52 to thepreregistration nip formed by rollers 82 and belt 36. Upon return fromthis subroutine, the routine next enters a FEED subroutine, shown inFIGS. 15a and 15b, in which the belt 36 is actuated to advance the firstsheet to a position on the exposure platen 24 defined by registrationgate 96. Thereafter, the copier 22 is actuated to initiate scanning ofthe original placed on the platen 24. Such actuation of the copier maybe performed by any suitable means, such as by closing the print switchSW1 of the copier shown in the Suzuki et al patent identified above.

While the copier 22 is scanning the first original placed upon theexposure platen 24, the feeder control routine immediately re-enters thePREFEED subroutine shown in FIG. 14 to prefeed a second original to thepreregistration nip formed by preregistration rollers 82 and belt 36. Byre-entering the prefeed subroutine immediately in this manner, ratherthan waiting for the completion of the exposure step, one maximizes theeffective copy rate obtainable, since otherwise both the prefeed andfeed subroutines would have to be completed between successive exposuresfor each document presented to the platen.

After the completion of exposure of the document on the platen 24, asindicated by the end-of-scan signal from source 286, the feed subroutineis re-entered to advance the second preregistered document to theexposure platen 24 while at the same time delivering the first documentfrom the platen to the receiving tray 168. The routine then successivelyre-enters the prefeed and feed subroutines to advance succeedingdocuments to the exposure platen, in each case waiting for completion ofexposure before entering the feed subroutine. When, as indicated by thetray sensor 258 in a manner to be described, there are no more sheetsremaining to be fed either from the upper tray 52 or the platen 24, theroutine deactuates the copier 22 and returns to the start to await thesubsequent actuation of the feeder print switch 284. Deactuation of thecopier 22 may be performed by any suitable means, such as by reopeningthe print switch SW1 of the copier shown in Suzuki et al U.S. Pat. No.4,009,957.

Referring now to FIG. 14, in the prefeed subroutine, which issuccessively entered to advance documents to the preregistration nipformed by registration rollers 82 and platen belt 36, an internal timer(not shown) of the computer 282 is first set to define a maximum timeinterval within which the leading edge of a document advanced from thetray 52 should reach the entry path sensor 260. As already mentioned, a"first original" prefeed time, preferably about 2.3 seconds, is used onthe first pass, while a shorter prefeed time, preferably about 480milliseconds, is used on succeeding passes. The subroutine then checksthe tray sensor 258 to determine whether any sheets remain in the uppertray 52. If there are no more sheets remaining in the tray 52, thisindicates that all of the sheets have been fed from the upper tray, andthe subroutine sets a "last pass" flag (not shown) internal to thecomputer 282 to record this fact. The subroutine then stops the timerthat was previously set and returns to the main routine shown in FIG.13.

If, on the other hand, the tray 52 still contains sheets, the subroutineenergizes the prefeed motor 200 to cause feed rollers 66 to advance thelowermost document to the preregistration nip. If the timer that waspreviously set counts down to zero before the leading sheet edge passesentry sensor 260, the subroutine stops the timer, deactuates the prefeedmotor 200 and jumps to the jam routine shown in FIG. 16, in whichdisplay 288 is energized to advise the machine operator of the existenceof a jam in the feeder 20.

If entry sensor 260 does sense the leading edge of the document beforethe lapse of 2.3 seconds or 480 milliseconds as the case may be, thesubroutine stops the timer and delays a further 100 milliseconds toallow the leading sheet edge to enter the preregistration nip and buckleslightly to ensure reliable preregistration. Thereafter, the subroutinedeactuates the prefeed motor 200 and returns to the main routine shownin FIG. 13.

Referring now to FIGS. 15a and 15b, in the FEED subroutine forcontrolling the drive of the platen belt 36, the prefeed motor 200,which was previously deactuated in the prefeed subroutine, is reactuatedfor 20 milliseconds to supply a torque pulse to the feed rollers 66.This pulse, as described above, energizes the feed rollers 66 with theirfull start-up torque to ensure separation of the bottom sheet from anyadditional sheet which may have passed through the , nip formed byrollers 66 and 70. Next, the platen belt 36 is energized by actuatingthe belt motor 220 and clutch 230, while the prefeed motor 200 isdeactuated immediately thereafter. Actuation of belt motor 220substantially concurrently with the momentary reactuation of feedrollers 66 ensures that belt 36 will begin to draw the sheet through thepreregistration nip before the leading sheet edge has a chance to"spring back" from the nip following its forced injection. Uponenergization, belt 36 advances the sheet that has been pre-fed to thenip formed with preregistration rollers 82 to a registered position uponthe exposure platen 24.

After a delay of 48 pulses from encoder 240, belt 36 should haveadvanced any document that was previously on the platen 24 to a positionat which it intercepts the light beam of the exit sensor 266. If thecurrent pass is any pass other than the first, the subroutineinterrogates the exit sensor 266 at this time to determine whether ithas been actuated. If it has not been actuated, this indicates a misfeedof the document previously upon the platen 24, and the subroutine jumpsto the ADF jam routine referred to above, shown in FIG. 16. If the exitsensor 266 does sense the exiting sheet, the subroutine delays a further16 pulses from encoder 240 and then actuates registration gate solenoid110 to raise the registration gate 96. Immediately thereafter, thesubroutine supplies a suitable signal to the belt motor 220 to reduceits speed to 1/5 of its normal speed of 75 inches per second, so thatthe sheet currently being advanced along the platen 24 to theregistration gate 96 strikes the gate at a relatively low speed.

Although it is preferable, from the standpoint of precision of control,to drive the belt at a low speed following the discontinuance ofhigh-speed drive, it is also possible to deactuate the motor 220entirely, so that the belt 36 continues to move because of its owninertia, and that of its drive elements, and coasts to a stop shortlyafter the registration gate 96 arrests the sheet on the platen 24. Insuch a mode of operation, the deactuation of belt motor 220 would be sotimed that the belt 36 is still moving at the time of sheet interceptionby registration gate 96, but at a speed substantially reduced from thatimmediately preceding motor deactuation.

After a further delay of 24 pulses from encoder 240 to ensure that thedocument has reached its registration position and that any initial skewhas been eliminated, the routine disengages the clutch 230 to disablethe belt 36. Belt motor 220 may be either likewise deactuated at thistime or, if desired, left running to reduce start-up time on succeedingpasses. At this point in the feed subroutine, the exit path should beclear in the area of the exit sensor 266 while the entry path should belikewise clear in the region of the entry sensor 260. Accordingly, onany pass except the first pass, the subroutine interrogates the exitsensor 266 at this time and jumps to the previously identified jamroutine if the sensor detects a sheet. Thereafter, on any pass exceptthe last pass, the subroutine interrogates the entry sensor 260 andjumps to the jam routine if that sensor detects a sheet at this time. Ifneither of the sensors 260 and 266 is actuated, the subroutine thensupplies belt motor 220 with a suitable signal switching it to itshigh-speed mode of operation, following which the subroutine returns tothe main program.

Referring now to FIG. 16, the jam routine is entered in response to thedetection of a jam in the course of the prefeed and feed subroutines inthe manner described above. Upon entering the jam routine, the computer282 actuates the jam display 288 to apprise the operator of theexistence of a sheet jam. In a manner known in the art, the jam display288 may simply comprise an indicator light or if desired may alsocomprise a coded digital display indicating the particular nature orlocation of the jam. After actuating the jam display 288, the routinechecks the entry and exit sensors 260 and 266 to determine whether theoperator has extricated any jammed originals from these locations. Whenthese sensors are clear, and when the operator has actuated the jamreset switch 290 by raising the feeder 20 a predetermined distance fromthe exposure platen 24, the jam routine deactuates the jam display 288and returns to the start of the main program shown in FIG. 13.

It will be seen that we have accomplished the objects of our invention.We have provided a document feeder for an electrophotographic copierwhich reliably registers documents at a predetermined position upon thecopier exposure platen. Our feeder produces copies with clearbackgrounds from smaller-than-normal originals and does not damageoriginal documents being handled. Further, our feeder has the sheetawaiting copying in a ready position in a feed nip adjacent to theexposure platen to minimize feed time, thereby to maximize the overallcopy rate, as well as to ensure reliable feed and minimize delayoccasioned by slippage. Our feeder minimizes discontinuities occasionedby changeovers of gripping surfaces, and is especially compatible with afeed belt which must remain stationary during exposure. Our feederdetects jams rapidly enough to prevent damage to originals being fed. Atthe same time, however, it does not declare a sheet jam prematurely uponinitial loading or improper placement of sheets in the document tray.

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of ourclaims. It is further obvious that various changes may be made indetails within the scope of our claims without departing from the spiritof our invention. It is, therefore, to be understood that our inventionis not to be limited to the specific details shown and described.

Having thus described our invention what we claim is:
 1. In a sheetfeeder having means for supporting a stack of sheets to be fed, meansadapted to be actuated to advance a sheet from said stack to a locationspaced therefrom, and means responsive to the absence of said sheet atsaid location after a preset time period following the actuation of saidadvancing means for providing an indication of abnormal operation, theimprovement comprising means for initially setting said preset timeperiod as a first time period for the feeding of said sheets to saidlocation and means for automatically and subsequently setting saidpreset time period as a second time period for said feeding of saidsheets which is shorter than said first time period.
 2. A sheet feederaccording to claim 1 wherein said second time period is set after thefeeding of a first sheet from a newly loaded stack of sheets.
 3. A sheetfeeder according to claim 2 wherein said second time period is setbefore the feeding of a second sheet from a newly loaded stack ofsheets.
 4. A sheet feeder according to claim 1 wherein said first timeperiod is greater than about 2 seconds.
 5. A sheet feeder according toclaim 1 wherein said second time period is about 0.5 seconds.